3rd generation partnership project (3GPP) long term evolution (LTE) evolved from a universal mobile telecommunications system (UMTS) is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas. In recent years, there is an ongoing discussion on 3GPP LTE-advanced (LTE-A) evolved from the 3GPP LTE.
Minimization of driving tests (MDT) is performed by venders for coverage optimization by using a user equipment (UE) instead of using an automobile. The coverage varies depending on a location of a base station (BS), deployment of buildings nearby, a user's usage environment, etc. Therefore, it is required for the vender to periodically perform the driving test, and a lot of costs and resources are consumed. The MDT is used by the vender to optimize a network by using the UE.
The MDT can be classified into a logged MDT and an immediate MDT. According to the logged MDT, after performing the MDT measurement, the UE delivers a logged measurement to a network at a particular time. According to the immediate MDT, after performing the MDT measurement, the UE delivers the measurement to the network when a reporting condition is satisfied. The logged MDT performs the MDT measurement in a radio resource control (RRC) idle mode, and the immediate MDT performs the MDT measurement in an RRC connected mode.
The vender can gather MDT measurements received from several UEs to create a coverage map which shows distribution of quality of service and service availability across an overall area in which the vender provides a service, and thus can utilize the coverage map for a network operation and optimization. For example, when a coverage problem of a specific area is reported from the UE, the vender can increase transmit power of the BS which provides a service of the area to expand coverage of a corresponding cell.
In the logged measurement, a granularity of the coverage map depends on a mobility of the UE. Since the mobility of the UE may change while the UE is on the move, the granularity of the coverage map may have a different value depending on a location. Due to an excessively high mobility of the UE, a coverage hole may occur if the granularity of the coverage map is significantly low in a specific location, which results in deterioration of efficiency of the coverage map. Accordingly, there is a need to provide a logged measurement method considering the mobility of the UE.